Live Closed Captions

Recent FCC regulations require that any content shown on television with closed captions must also be captioned when streamed online. IBM Video Streaming or Video Streaming for Enterprise customers with supported encoders now have the option of passing their captioned content through to the IBM Watson Media player.

Once a channel has caption support enabled, the IBM Watson Media platform and player will automatically detect and display the 608/708 closed captions. Viewers can mouse-over the player to reveal the CC button where they can toggle the captions on and off. Caption data is preserved and synced with the recorded file for on-demand viewing.

Note: Closed Captions are only available for our Enterprise Pro Broadcasting users.

For additional information on closed captions, please see the related blog post:

Captions Off

Captions On

How do closed captions work?

It is important to first make the distinction between “Closed Captions” and “Subtitles”. Closed Captions serve as an accessibility feature for the deaf or hard of hearing, while Subtitles are an internal viewer/listener feature.

Examples: Actions like “window slams shut” or “footsteps approach” are present in closed captioning to explain what is happening. Subtitles are used simply when translating speech-to-text, like when providing French subtitles for English content.

Embedded captions usually contain the following caption formats: CEA-608, CEA-708, DVB-T, DVB-S, WST. These formats can be embedded into the video stream, or written directly into a video file.

Separately stored captions usually contain the following formats: DFXP, SAMI, SMPTE, TTML, XML, WebVTT, SRT, SCC, EBU-STL. These formats transmit caption data to a player beside the video, as opposed to embedded within the video. This is most common with browser-based video playback (Flash, HTML5).

Embedding Closed Captions: Live Streaming

The following are a few of the most commonly used methods and formats for delivering embedded closed captions.

CEA-608

Originally used as the standard for analog broadcasts, but can be embedded in digital broadcasts. 608 data is inserted in the Line 21 data. Due to character limitations, 608 captions are limited to encoding in English, Spanish, Portuguese, French, Italian, German and Dutch. There are only two available fields for languages in line 21 This is often considered an older delivery method.

CEA-708

Introduced for use with digital broadcasts, this newer delivery method has many more advanced appearance standards. 708 data is inserted via the H.264 stream.

RTMP onCaptionInfo metadata

This is an Action Message Format (AMF) onCaptionInfo with a type of "708". This caption type contains Base-64 encoded CEA-608 or CEA-708 caption data.